For example, Japanese Patent Application Publication Number 2012-135095 A discloses an LED lighting device. In this LED lighting device, when a second switching device of a voltage step-down portion is short-circuited, a voltage applied across a light source portion exceeds a prescribed voltage. In this case, a first switching device of a voltage step-up portion is inactivated. As a result, a switch element is turned off and an electric current from a DC power supply portion flows through a current-limiting element, thereby limiting a load current flowing through the light source portion to prevent an excess current from flowing therethrough.
However, in the LED lighting device, there is a problem that the power consumption in the current-limiting element increases. In a period of time (see “Ta” in FIG. 2) when the booster portion is activated and the voltage down portion is inactivated, the switch element is in off-state and an electric current flows through the current-limiting element (a thermistor). In this case, a resistance value of the current-limiting element largely increases and a voltage across the current-limiting element increases as well. As a result, the power consumption in the current-limiting element increases. In addition, there is a concern that the booster portion cannot perform a normal step-up operation, because the voltage across the current-limiting element increases and thereby an input voltage to the booster portion may decrease to fall below a rated input value thereof.